This disclosure relates to a tube fitting for connection of a tube to a fluid system component particularly suitable for automotive fuel injection systems. It further relates to such a fitting having a seal surface defining the interface between the connected tube and associated system components.
Modern automotive fuel systems include fuel components that deliver liquid fuel to the engine injectors within the engine compartment. These systems are under high pressure and include fuel rails or manifolds and connecting metal tubular fuel lines. The junction between such lines and the associated components include fittings which provide a fluid tight connection that withstands the rigors of the operating environment, i.e. constant vibration, high internal pressure and high temperature.
The tubing is usually high grade stainless steel which is resistant to the fuel being delivered. The tubing is usually bent into specific shapes to extend between junctions where it attaches by a threaded fitting to an associated receiver.
Typically the connection includes a receiver or body secured to the system component that defines an annular seat against which the shaped end of the tube is compressed. A threaded nut surrounds the tube and engages with receiver body. The tube includes an enlarged end form configuration shaped to abut the seat surface in fluid tight relation. The threaded nut urges the end configuration into sealing engagement with the seat.
Because of the hardness of the tube material, usually stainless steel, and the vibration associated with engine operation, some fittings include a separate seal element interposed between the end of the tube and the seat of the receiver. This seal element may be made of material having low friction properties, such as copper alloy which possesses durability under extreme vibratory conditions. It is also a material unaffected by the fuel within the fluid system.
In some instances, the separate seal element is fixed to the tube end form by mechanical deformation. This is, however, a separate processing step that adds to complexity and manufacturing cost.
The presence of a separate seal element complicates the manufacture of the system components and also the assembly process. Often the tubing and other system components are provided by different suppliers. The presence of a separate seal element must be monitored and assured at the final assembly stage to confirm reliability, and system integrity.